Conventionally, for the purposes of improving fuel efficiency of an automobile, reducing an environmental load, and the like, an automatic idle-stop system, which automatically performs idle-stop when a predetermined condition is satisfied, has been developed. For example, with a method for bringing a starter pinion into meshing engagement with a ring gear and a starter controller described in Patent Literature 1 described below, when an rpm of the ring gear is within a predetermined range and a direction of rotation is forward, the pinion gear is brought into meshing engagement with the ring gear. A meshing state between the pinion gear and the ring gear in an early stage is realized.
In Patent Literature 2 described below, when a direction of rotation of a ring gear which rotates reversely changes to be forward again, the pinion gear is brought into meshing engagement.